The present invention relates to high speed printers and more particularly to high speed impact printers in which a plurality of magnetic actuators are arranged in a closely spaced array and are repeatedly energized in varying patterns to effect printing from moving type elements, e.g., type elements carried on an endless rotating band.
In high speed band printers, an elongate array of hammers are typically employed to drive paper against a type font embossed on a continuously moving metal loop, the "band." An inked ribbon is normally interposed between the paper and the print elements. To effect printing in this manner, the operations of the hammers must be timed to occur when the desired character is in registration with the respective columnar position on the paper. While most band printers are arranged, e.g., by means of the character spacing on the band, so that it will not be necessary to simultaneously print adjacent characters along the line of print, the magnetic actuators for the hammers, because of their physical size, must typically be arranged in multiple linear banks with successive hammers being driven from the differing banks in rotation. One such hammer and actuator arrangement is disclosed in greater detail in copending coassigned application Ser. No. 509,925 filed on July 1, 1983 by James R. Moss.
With such a banked construction, it is entirely possible that physically adjacent magnetic actuators may be energized during the same print cycle. Since the magnet coils will typically be in close physical proximity, magnetic interaction may occur and the effects caused by this interaction may take any of several forms, each of which can distort the response time of the actuator. Since the type font is continuously moving, it will be readily understood that any change in the response time of the actuator will result in a change in position of the character as printed on the paper. In the particular case of band printers, this variation in response time may cause a displeasing lateral shifting of the printed characters with respect to their neighbors.
While various attempts at magnetic shielding have offered some improvement in these interaction effects, the dense physical packing typically required for the magnetic actuators in band printer has effectively precluded any complete solution by this approach. Accordingly, some prior art printers have gone to a system in which operation of a given actuator is inhibited if adjacent actuators are being energized on the same print cycle. As will be understood by those skilled in the art, however, this solution imposes a severe penalty in throughput since the system must wait for another opportunity to strike the same character. The delay thereby incurred will be dependent upon the distribution of characters on the band and the speed of the band so that multiple passes of the font may be required. Such systems are for example, disclosed in U.S. Pat. No. 4,286,517 and U.S. Pat. No. 4,278,021.
Among the several objects of the present invention may be noted the provision of a high speed impact printer which provides a high degree of columnar alignment; the provision of a high speed band printer employing a dense array of magnetic actuators in which magnetic interaction between actuators does not appreciably disturb columnar alignment; the provision of such a band printer which has high throughput; the provision of such a band printer which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.